1. Field of the Invention
The present invention relates to solid-state laser technology. More specifically, the present invention relates to techniques and materials for joining laser components.
2. Description of the Related Art
Recent advances in high-energy diode-pumped solid-state lasers have facilitated extensive developments in the architecture of laser components such as laserable slabs, rods and disks. Solid-state laser slabs typically include a thin planar solid-state gain medium (core plate) that is encapsulated by a solid crystal cladding. The core plate, primarily having a rectangular cross-section, is a key laser component affecting beam quality at high energy levels. Commercial laser slabs are typically comprised of single crystals, such as Yb:YAG (ytterbium doped yttrium-aluminum-garnet) and Nd:YAG (neodymium doped yttrium-aluminum-garnet), or polycrystalline transparent ceramics, such as Y3A15O12. The core plate often includes two undoped input and output sections bonded to a doped central section. The bonded core is then structurally integrated with a peripheral crystal plate cladding made from material (such as Sapphire, Spinel, or related ceramics) having a step-index refractivity interface with the core to suppress parasitic oscillations that deplete energy in the core gain medium. In addition, a laser slab may also include various prisms joined to the input and output sections for inserting pump light and extracting laser energy from the slab.
These multiple components need to be joined together without introducing any optical defects in the laser slab. Conventionally, laser components are joined using diffusion bonding. Diffusion bonding typically includes placing the joining crystal or ceramic units in intimate contact and applying external pressure and heat, so the units can be bonded together uniformly throughout. The pressure and temperature can be constant or variable, including various programmable cycles. Various pressurization techniques include those using “hot presses”, hydrostatic systems, statically indeterminate systems (which develop intrinsic thermal stresses when heated), and the techniques based on van der Vaals force-assisted optical contacting. All these pressurization techniques, as well as precision grinding and polishing, are commonly used in the fabrication of core components.
Diffusion bonding of laser components, however, meets enormous difficulties, particularly when bonding dissimilar materials such as YAG and Sapphire. The thermal (CTE) mismatch and high temperature processing (about 1200-1700° C.), as well as the high elastic moduli of Sapphire and YAG, result in high interfacial thermal stresses localized at the slab ends. The crystal dissimilarity (hexagonal vs. cubic) and lattice mismatch between Sapphire and YAG substantially complicate the solid phase interaction between the dissimilar crystals. These difficulties lead to imperfect and low strength interface formation with strong propensity to delamination, reduced thermal conductivity at the imperfect interface, and energy leaks. In addition, diffusion bonding requires very high precision polishing of the components to be joined. This is a time-consuming and expensive process.
Glass soldering is a well-known technique widely used in electronics and micro-optics for sealing of cathode tubes, liquid crystal displays, micro-optic components, hermetic encapsulation of glass and metal electronic packages, etc. Glass soldering typically uses high temperature melting glasses. In spite of the existing popularity of glass soldering, its application for laser components meets substantial limitations, primarily associated with the high temperature processing, which causes a haze appearance in YAG and increases its light absorption and scattering.
Hence, a need exists in the art for an improved system or method for joining laser components that is more effective and less expensive than conventional approaches.